old color headgreenspun.com : LUSENET : Large format photography : One Thread
Anyone know much about color filtration? (for B&W use) I just purchased an ancient Chromega color head "D" series (along with a beautiful D4 chassis), and am working on the assumption that the filters have faded miserably over the years. I haven't had a chance to use it yet, though. I know that replacements are no longer available...
I have come up with the following solutions and any feedback would be welcome.
1) Cut out an Illford Ilfochrome color filter .40 magenta (for example) to size, as a replacement filter
2) Rely on the old filters, but place a 2 1/2 contrast filter in the base of the mixing chamber to raise the magenta "baseline" up to a usable level. The additional magenta from the old filter would then just add contrast on top of that.
3) Do some combination of both. Anyone know if color filters are additive (or would that be subtractive) in this way?
4) give up and use filters under the lens (sacrificing some optical performance)
-- Chris (firstname.lastname@example.org), June 27, 2001
Chris: I would give the old filters a try before tossing them out. First thing though, I would put new bulbs in the head. Old bulbs shift color as they age, depending on the amount of use. Develop your own set of numbers for contrast control. Dialing in 30 points of magenta or yellow on your enlarger may be different than 30 points on another head. It doesn't matter as long as the results are repeatable and you know how much filtration you need.
-- Doug Paramore (email@example.com), June 27, 2001.
You deffinitly will want to give the original filters a try first. They are most likely Dichroic filters-that is what they used in most of their color heads. Dichroic filters are coated glass and they last a lot longer than gels(by many magnitudes). Putting a gel filter in front of the light would last about one printing sesion. If you really do have to replace the dichroic filters in the Chromega and you can't get them from the factory then go to Edmunds Scientific and get a magenta and a yellow dichroic filter and put them in place of the originals. And when you open up the chromega head you will see that the unit is made in a way that will lend easy repair or modification. In other words, it does not have to be exact. The only crucial point is that you use Dichroic filters.
-- David Vickery (firstname.lastname@example.org), June 27, 2001.
Chris, Ditto on the previous comments. A filter will fade in the range it is used - usually in the 30-80 cc range. Zero and max. are still attainable, as is everything in between. The fact that the numbers are not accurate will not be a problem in B&W.
-- Bruce Wehman (email@example.com), June 27, 2001.